Production of dicarboxylic acids or anhydrides thereof



l. E. LEVINE March 23, 1948.

PRODUCTION OFDICARBOXYLIC ACIDS OR'ANHYDRIDES 'I'HEREOF Filed May 30, 1945 INVENTovV IQVING E. LEVINE ,rf/md ATTORN EYS l mentes 1m23.194s v Y Y *y n 21,438,369

'UNITED STATES PATENT' -OFFICE: 2.43am

PRODUCTION lF DICABBOXYLIC ACIDS 0R ANHYDBIDES THEREDF Irving E. Levine. Berkeley, Calif., assigner to California Research Corporation, San Francisco, Calif., a corporation of Delaware Application May 30, 1945, Serial No. 596,645

l 14 Claims. (Cl. 26o-342) This invention relates to a process for producsubstituted benzenes may be utilized. provided ing phthalic anhydride or phthalic acid from a4 that the vapors therefrom contain a maior promixture of aliphatic substituted benzenes. portion of an ortho di-alkyl benzene. For ex- More particularly, the invention is directed to ample, mixtures of di-alkyl benzenes in which the a process for producing phthalic anhydride or 5 alkyl groups may be ethyl, normal propyi or isoacid from a mixture of polyalkyl benzenes conpropyl, or mixtures 0f these alkyl benzenes with taining a predominant or major proportionv of each other or of methyl, etlhy1 mdf propyl sub- Ortho benzenes, but also Substantial stituents or of any of the foregoing with diamounts of meta or para Dolylkyl benzenes. methyl substituted benzenes may be utilized 'Ihe invention provides a process of producing l0 where a content of more than 50%, and preferrelatively pure phthalic anhydride in good yields ably 70% to 95% 0f ortho di-alky] benzenes is from relatively impure ortho di-alkyl. benzenes obtained in vapors therefrom. Small amounts as a xylene mixture containing 5-30% of meta of naramnic or nanhthenic hydrocarbons or and Para xylenes in admxtule With 01' tho xylenemono-alkyl benzenes in mixtures such as the fore- An object of the invention is to provide a new going are not precluded. and improved process for partially oxidizing mix' It has been discovered that phthalic anhydride tures of alkyl benzenesand for facilitating sepaa be ro uced from mixture of a l benzenes ration of the oxidation products so produced to eausepsulh as the foregoing gy parlny oxidiz obtain phthalic anhydride or phthalic acid.

ing the ortho substituted aliphatic benzenes to phlenllygdgfffg igigllggclnl Dhthalic anhydride and preferentially removing ing a major propotion of ortho Xfylene and to the non-ortho alkyl lnenzenes by simultaneously eliminate the meta and para xylenes by se1ec selectively over-oxidizing these constituents at tively rupturing the ring by chemical oxidation. least to fhe pomt of Img rupture and Preferably other Objects and advantages of the invention substantially to carbon dioxide and water. The will be apparent from the follpwing disclosure. Partially Oxldzed Ortho alkyl benzene8-are then The aglkyl benzenes from which phthanc an separated from the mixture of combustion prodhydride is produced according to the present incts by condensing the Dhthaic anhydride and vention are exempliied by a mixture of ortho, separating, in the form of a gasoxidation prodmeta and para xylenes containing more than 30 ucts from the other alkyl benzenes. Thus, the desirably from about to 95% by weight, and present invention. in its preferred embodiment, preferably approximately l to 90% of ortho involves simultaneous oxidation of the three xylene. \Other mixtures of vaporizable aliphatic xylenes, as follows: K

O f CH: Vapor phase I h 0 -n O H 0 Ort oxylene -I- i oxidation catalyst i i omy Mt l +0 vapoerp insuture--sCO +110 ene r r e "y oxidation myst p P l 0 Vpo---erphase in l1 til -9 C0 -I-HO ara e c r r re xy n oxidation catalyst g p assenso It will be observed that ortho xylene in the xylenemixture is only partially oxidized according to the present invention, and the reaction is stopped short of ring rupture and substantially at the phthalic anhydride stage. However, in the same reaction zone the meta and para xylenes are selectively over-oxidized at least to the point of ring rupture and preferablyto carbon- The meta and para xylenes,

dioxide and water. which might otherwise yield aromatic oxidation products sufilclently similar to the phthalic anhydride from ortho xylenefto make separationk and purication extremely diillcult, are thus preferentially eliminated from the reaction mixture by over-oxidation and maintaining the combustion products thereof in a gaseous Phase. The phthalic anhydride is then easily recovered by I selective condensation or other suitable processes.

It is known that ortho xylene may be partially oxidized to yield various reaction products, including phthalic anhydride. However, the selective over-oxidation of meta and para alkyl benzenes to eliminate these components from mixtures with ortho alkyl benzenes while only partially oxidizing the ortho alkyl benzenes to phthalic anhydride is believed new and unobvious. For example, it has been shown that aromatic hydrocarbons with side chains are oxidized from 1,000 to 6,000 times faster than benzene (Catalytic Oxidation o Organic Compounds in Vapor Phase,` by Marek and Hahn, page 395); yet by the present invention' the aliphatic side chains of the meta and para alkyl benzenes can be substantially completely oxidized and the benzene ring ruptured, while oxidation of the ortho alkyl benzenes is preferentially stopped without breaking the bond between the ortho alkyl carbon atoms and the benzene ring. Further, Burgoyne (Proceedings of the Royal Society, volume A-174, page 379, `1939) concluded that in an oxidation under pressure the order of increasing reactivity is para, meta, ortho, suggesting that as between these three components the more reactive ortho, if any, would be selectively over-oxidized. Accordingly, the discovery that (even though alkyl benzenes may be more easily oxidized than benzene, and despite the report that ortho alkyl benzenes are more reactive than meta and para alkyl benzenes in oxidation un' der pressure) the meta and para alkyl benzenes may be selectively over-oxidized to the point of ring rupture, and even to carbon dioxide and water, in the presence of a predominant proportion of ortho alkyl benzene without a corresponding destruction of the ring or of its bond to ortho alkyl carbon atoms directly" attached thereto, is believed unobvious.

Briefly described, the process of the invention comprises vaporizing a mixture of aliphatic substituted benzenes of which a maior proportion has two aliphatic groups positioned ortho to each other on the benzene ring and a substantial proportion of the hydrocarbon mixture comprises aliphatic benzene hydrocarbons other than ortho aliphatic substituted benzenes, partially oxidizing the ortho-substituted aliphatic benzene vapors to phthalic anhydride, simultaneously selectively over-oxidizing the other aliphatic benzene vapors inthe mixture, at least to the point of ring rupture, to produce over-oxidized combustion products readily separable from the phthalic anhydride, and separating phthalic anhydride from the combustion mixture. i

The foregoing partial oxidation and selective over-oxidation are carried out in accordance with A be understood that this invention preferably by mixing the vaporized alkyl benzene vapors withan excess of an oxygen-containing gas, such as air, and contacting the vapor-oxygen mixture at elevated temperatures with a metal oxide which is an oxidation catalyst, such as a vanadium oxide catalyst. The reaction is exothermic and heat is removed by any suitable means 4to control temperature of the reaction. Catalyst temperature preferably is maintained in the zone of red heat. Such relatively high temperatures, together with a large excess of the oxygen-containing gas, serve to form the phthalic anhydride quickly and to carry the oxidation of the meta and para alkyl benzenes not only to .the point of ring rupture, but at least in major part to carbon dioxide and water. Since the selective over-oxidationmay be carried only to the point of ring rupture, catalyst temperatures as low as about 800 F. are operable. However, a catalyst temperature in the dark red heat range is desirable and from a dark blood red to a dark cherry red, as indicated in Marks' Mechanical Engineers Handbook (2nd ed., page 297) is preferred (i. e., 990 F. to 1175 F.). It should be clear that the entire catalyst bed need not be maintained at this high temperature level. Only a relatively short zone, sufficient to insure selective overoxidation at least to ring rupture and preferably substantially completely to carbon dioxide 'and water, need be in the dark red heat range (e. g., 1/3-1/1 of the catalyst bed). Likewise, it is to temperatures referred to above are catalyst temperatures as measured by a thermocouple in the catalyst bed.

A large molar excess of oxidizing gas is utilized in the process. Air is preferred, although mixtures of oxygen or air with nitrogen, carbon dioxide or other inert or non-oxidizing gases may be utilized. Desirably, the molar ratio of air to hydrocarbon should be at least about 50 to 1, and preferably from 50:1 to 150:1. A still higher ratio of air to hydrocarbon (300:1 or more) may be utilized with an adequate system for recovering the product in the resulting more dilute gaseous mixture. In general, corresponding ratios of other voxygen-containing gases are utilized. The oxygen-containing gasshould be in meta and para xylenes, together with other hy' drocarbon impurities, are selectively over-oxidized mainly to carbon dioxide and water, these impurities are eliminated and phthalic anhydride may be easily separated by mere cooling and condensation to yield a product containing no more than about 2% and even less than 1% aromatic impurities. For example, the hydrocarbon combustion mixture may be passed from the oxidation zone to relatively large air cooled chambers where the temperature of the gaseous mixture is reduced I to below the phthalic anhydride frost point (i. e.,

the temperature at which phthalic anhydride condenses as a solid) whereby the phthalic anhydride solidies as crystals in the cooling chamber. These crystals are collected in the cooling crude condensate, e. g., fractional aaaaaee chambers and separate from the over-oxidized products of meta and para alkyl benzenes, as well as from the other combustion products.

In those operations where the oxidation of aromatic hydrocarbons other than ortho alkyl substituted benzenes is carried to the point of ring rupture but a substantial portion is not completely oxidized to carbon dioxide and water, small amounts of the residues of the ruptured rings, as well as other impurities, may be precipitated in the cooling chambers with the phthalic anhydride, thereby generally decreasing the purity level of the crude condensate. However, even in this type of operation the main impurities are nonaromatic and dier in chemical kind from phthalic anhydride byy reason of the selective over-oxidation and ring rupture. Any suitable method may be utilized for further purifying the crystallization from a solvent, such as mixed xylenes, or fractionation by distillation.

The initial recovery of phthalic anhydride from the combustion gases and separation from the over-oxidation products of meta and para Xylenes may be accomplished in various ways, including washing the mixture of gases with a suitable solvent or chemical extractants or byproper selective absorption. However, the best method at present appears to be cooling and condensation as above described. The gaseous mixture is preferably cooled to a point within the range between the phthalic anhydride frost point and the water dew point. The phthalic anhydride frost point may be defined as that temperature at which phthalic anhydride first begins to separate out as a solid phase. The water dew point is that temperature at which moisture lrst begins to condense as a liquid phase. Where there is no objection to the formation of phthalic acid in the condensate, or, if this should be desired (e. g., to increase the ultimate recovery of desired product), the gaseous reaction product may be cooled below the dew point with the consequent precipitation of water and reaction thereof with anhydride to form phthalic acid,

The phthalic anhydride frost point varies with the phthalic anhydride content of the gaseous mixture, which in turn is a function of other process variables, such -as air-hydrocarbon ratio,

ortho xylene content of the origin-al hydrocarboni mixture, etc. Likewise, the water dew point is a function of such variables, as `well as of the humidity of the original oxidizing gas. Determinatlon of these two points (phthalic anhydride frost and water dew points) for any given operating condition'is readily determined by those skilled in the art and it is believed unnecessary to here designate specific temperature. However, cooling to temperatures lower than prevailing atmospheric temperatures is usually unwarranted, and an upper temperature limit for the gases leaving the'inal stage of a cooling and condensing system is at presentfound to be from about 100 to 150 F.

. Various forms of apparatus may be used for carrying out the foregoing process. One which has been found suitable is shown somewhatr diagrammatically in the drawing. 'I'he apparatus comprises three principal umts or sections; namely. an air feed and hydrocarbon vaporization unit which vaporizes the hydrocarbon feed and mixes the vapors with air to form a reaction mixture; a temperature regulated catalyst chamber in which the desired conversion of the foregoing reaction mixture is effected; and a phthalic anhydride condenser for separating the reaction products.

More specifically, air is admitted to the vaporization unit through inlet III controlled by a main regulator II, flows through a calibrated orifice I2 for determining volume of air fed, and is then divided into a primary and a secondary air stream. The primary air stream flows through conduit I3 and vaporizer I4 where the hydrocarbon feed stockis vaporized into the primary air. Secondary air from metered orifice I2 ows by way of conduit I5, secondary air regulator I6, and line I1 to chamber I8 which also receives, by way of conduit I9, the air-hydrocarbon 4mixture from vaporizer I4. 'I'he two air streams are blended and lmixed with the hydrocarbon vapors in chamber 8.

As here shown, hydrocarbon vaporizer I4 comprises a steam jacketed liquid hydrocarbon container 2I provided with a sintered glass plate 22 at its lower end serving as a bottom for container 2| partially filled with alkyl benzenes 23. 'I'he primary air thus is dispersed into fine bubbles or streams by the sintered glass plate 22 and ows through the liquid phase alkyl benzenes 23, forming the air-hydrocarbon mixture which is nally diluted and mixed with secondary air in chamber I8.

Catalyst chamber 24 is provided with a preheating bed of aluminum turnings 26 further to mix the gases and bring them to desired temperature prior to entering catalyst bed 21 wherein the desired reactions are effected. Any suitable foraminous means 28 for supporting the catalyst bed 21 may be provided at the lower end thereof in the bottom of chamber 24. The gaseous reaction mixture flows from mixing chamber I8 through preheating bed 26 into the catalyst bed and is discharged from the catalyst chamber through conduit 29 to an air cooled condenser 3I Where the temperature of the gases is lowered sufficiently to cause phthalic anhydride to precipitate as needle-like crystals. The remaining components of the reaction mixture are discharged from condenser 3| and may be passed through a suitable meter 32.

Catalyst chamber 24, as here illustrated, comprises an inner catalyst tube 32 surrounded by an outer sealed container 33 for a liquid mercury temperature regulating bath 34 which only partially lls the container but preferably is maintained at a. level as high as the catalyst bed. 'Ihis mercury bath serves to remove heat of reaction from the catalyst bed 21 and, in` so doing, boils and is vaporized. The rising mercury vapors of partially filled container 33 heat the bed of aluminum turnings 26 and bring the hydrocarbon vapor feed at least up to reaction temperature and usually approximately tothe mercury bath temperature. Since the reaction is highly exothermic, excess heat must be removed from the system, and this is here accomplished by providing a condenser 36 for mercury vapors from cooling bath 34. Water, steam or any suitable iiuid may be utilized for condensing the mercury vapors and 'carrying offthe excessfheat of reaction by indirect heat exchange. 'I'he mermined pressure. 'I'he boiling temperature of the ered by reducing the nitrogen pressure. The temperature of the catalyst bath can thus be measured either directly or determined by the existing pressure in the boiling mercury system. Suitable means for directly measuring the temperature of the beds in the catalyst tube 32 is preferably provided and is here shown as a thermocouple 31 which is slidable longitudinally throughy a tube 38 sealed at its inner end 39 and passing centrally through catalyst bed 21.

Any suitable means (not shown) for .bringing the catalyst chamber up to reaction temperature may be provided.l One convenient device comprises electric strip heaters mounted on sealed container 33.

To illustrate in detail the process 'of this invention and to guide those skilled in the art in the practice thereof, the followingillustrative data and examples of processes, which may be carried out in the foregoing apparatus, are subl mitted.

Example 1 A xylene feed stockhaving a boiling range of about 288-296 F., a specic gravity of about .8825, containing approximately 85% by volume of ortho xylene and about by volume of mixed meta and .para xylenes is passed in vapor phase through a catalyst tube containing vanadium oxide on aluminum granules, at the rate of .12 mois per hour. The xylene vapors are mixed with 4,950 cc. per minute of air (12.4 mols of air per hour) and the hottest portion of the catalyst bed is maintained at about 1000 F. Air-hydrocarbon ratio is thus approximately 103 mols of air per mol of hydrocarbon, and this mixture was Example 2 Utilizing the same mixed xylene stock with a feed rate of .063 mol perhour and an air rate of '1.0 mois per hour, catalyst temperature was regulated at about 980 F. by a boiling mercury bath at approximately 950 F. Air-hydrocarbon ratio (molecular) was about 111 andcontact time about .17 seconds. A yield of approximately 87% phthalic anhydride resulted.

Example 3 An additionalrun, utilizing a. feed stock and process conditions substantially like those of Example 2, except that the hydrocarbon feedrate was .066 mol per hour, yielded 82% phthalic anhydride. y

Example 4 With a boiling mercury .bath temperature of 950 F., a catalyst hot zone temperature of 1080 F., and a contact time of approximately .07 seconds, an 86% yield of phthalic anhydride was obtained from a mixed xylene feed stock of' substantially the same composition as in Examples 1 and 3.

Example 5 Vapors of naphthalene and thev foregoing xylene feedstock are mixed (e.'g.`, equal, parts), diluted with air and oxidized in vapor phase substantially' as disclosed in Eixample 1. A good yield of phthalic anhydride and selective overoxidation of meta and para xylenes are obtained.

The yields in the foregoing examples are based on the amount of phthalic anhydride as it is actually condensed from thecombustion mixture. Yield is based on the weight of this product and is calculated as per cent of the weight of ortho xylene in the feed.

Despite the fact that the original feed stock in the above example contains about 15% of hydrocarbons which are here regarded asv impurities, the phthalic anhydride recovered by Lthe foregoing processes has been found to be relatively low in organic impurities. Most of these impurities are products of ring rupture, and not more than about 1% of aromatic impurities is found in the phthalic anhydride crude condensate, thereby indicating that the meta and para xylenes are substantially entirely over-oxidized at least to the point of ring'- rupture, while the f partial oxidation of the ortho xylene is preferentia-lly stopped at the phthalic anhydride stage to give good yields of this desired product.

It should be observed that maintenance `and control of reaction temperature is facilitated by selectively over-oxidizing the meta and para components of the reaction mixture to therebyy provide a relatively large positive heat input tol the reaction chamber without the necessity of supplying this extra heat atthe cost of ortho xylene v,with resulting loss of phthalic anhydride product, This heat input serves to minimize minor variations in heat formation or heat transfer rates which might otherwise occur, as well as to maintain the hot spot in the relatively high temperature range presently preferred. This extra heat also may be derived in part from other hydrocarbon impurities, such as ethyl benzene or parailins boiling in the same range as'the xyleness` Thus, the feed stock may consist of: parts of which fuses in a coherent mass. The fused mass .l

was broken and screened to pass 14 mesh andbe retained on a 30 mesh screen. This screened product yielded a catalyst bed with about 48% voids. The catalyst utilized in Examples 2 to 4 was prepared in a similar manner, but the final oxide coating was composed of approximately 60% vanadium oxide, 30% molybdenum oxide and 5% manganese oxide on 20 mesh aluminum. Other metal oxide catalysts for vapor phase oxidation may be utilized within the spirit of this invention, since the catalysts per se are not a part of this invention and various catalysts of this type are well known. Likewise, other cataiystsupports may be substituted for the aluminum, for example, silicon carbide. or other inert hillsi melting oxidation resistant granular materi Non-porous catalysts are preferred in order that the control of the selective over-oxidation X featured by this invention may be facilitated. -By "non-porous catalyst as here usedvit is intended tol designate those catalysts in,which the e'ective catalyst area is limited essentially to the outer surfaceportion of the catalyst granule; i. e., a catalyst in which the catalytic action takes rplace in or on the outer surface region, not in the deeper interior portion of a macroscopic catalyst granule or the like.V Porous catalysts, though not precluded, have been found less selective and tend to increase over-oxidation of the I 7 ortho xylene together with the meta and para xylenes.` To the extent this occurs, one primary mols of the meta and para compounds over-oxidized, to mols of orthoV di-alkyl benzene overand a minoi but substantial proportion of alkyl Y 99o .to about 1175 F.. and separating said benzene ortho dicarboxylic acid anhydride from said oxidized gases.

2. A process. of producing phthalic anhydride which comprises vaporizing a mixture of xylenes containing a major'proportion of ortho xylene benze'ncs selected from the group consisting of meta and para. xylnes, converting ortho xylene in said vapors tojphthalic anhydride byoxidation of the ortho alkyl 'groups with a vanadium.

oxide catalystl at a temperature o1 from about 800 F. to about 1175o F., concurrently ru'pturing the ring of said meta and para xylenes by selective over-oxidation of their vapors with a vanadium oxide catalyst at a temperature of from about 800 F. to about 1175*" F.,-said concurrent oxidation reactions being effected with'a molar excess of air in the ratio of` from about 50 to about 150`mols of air per Amoi of hydrocarbon mixture, separating phthalic anhydride` from at vleast a portion of over-oxidation products of said meta and para-xylenes by selective condensation oxidized, is greater than the ratio of the 'molar- 1 concentration of meta and para constituents in the vapor. to the molar' concentration'of. ortho alkyl benzene therein; Stated mathematically,

vselective over-oxidation of meta and para xylene occurs when mol. mdt p-xylene over-oxidized' mol.- o-xylene-over-'oxidized molar conc. m- & p-xylene in vapor 1 molar conc. o-xylene in vapor As previously noted herein, the invention' em' braces selective oxidation of mixed allwl benzenes other than xylenes. Likewise, selective overoxidation of meta and para xylenes or other a1- kyl benzenes in admixture with naphthalene vapors, ortho di-alkyl benzenes, and air may'be effected as'here disclosed.

preferably the molarquantity of alkyl Abenzenes should at least equal that ofthe naphthalene in the hydrocarbon vapors.

Although this invention has conditions have-been described, various altera- In such a process,A "the orthoalkyl component should be the majorV constituent ofthe alkyl benzenes present and `been illustrated with specific embodiments and preferred process from the gaseous reaction products. and separating said condensed phthalic anhydride from residual over-oxidation products by distillation.

3. A proc'ess' of producing phthalic anhydride which comprises vaporizing Aa mixture of aliphatic substituted benzenes having aliphatic radicals of from 1 to 3 carbon atoms, said mixture containing a major proportion of -ortho dialkyl 'benzenes and a minor but substantial proportion of alkyl .benzenes selected from the group conf sisting of meta and para dialkyl benzenes, convertingorthof alkyl benzene vapors in said mixture to phthalic anhydride by oxidation of the ortho alkyl groups .with a vanadium oxide catalyst at 'a temperaturel offrom about 800 F. to

about'1175f F., concurrently'rupturing the ring of said meta 'and' paraalkyl benzenes in said vapors by selective over-oxidation with a vanadium Eoxide catalyst at a temperature of from about '800F. to about 1175 F., said concurrent oxida- I 4tionreactionsbeing effected with a molar excess of air in thev ratio of from about'50 to about 150 mols of air perfmol of hydrocarbon, separating phthalic anhydride from at lleast a portion of over-oxidation products of said'meta and para alkyl benzenes by selective condensation from tions utilizing the principles thereof will occur to those skilled in the art, and it is to be understood that the invention .may be otherwise embodied or practiced within the scope of the appended claims.

Iclaim:

1. A process of manufacturing a benzene ortho dicarboxylicY acid anhydride by oxidation in va- -por phase of a mixture of aliphatic substituted benzenes having aliphatic radicals of 1 to 3 carbon atoms, a major proportion of said aliphatic substituted benzenes having two aliphatic groups positioned orthoto each otherv onl the benzene ring and a minor but substantial proportion having meta and para aliphatic substituents, said process comprising the Vstepsv of oxidizing the ortho aliphatic substituted benzenes to a benzene ortho dicarboxylic acid 'anhydride and simultaneously selectively over-oxidizing said meta and para aliphatic substituted benzenes at least to the point of ring rupture by passing said mixture in vapor phase over a vanadium oxide catalyst at a catalyst temperature Vof from about the gaseous reaction products and separating said condensed phthalic anhydride from residual over-oxidation products by distillation.

4. A process of manufacturing phthalic anhy-` dride from a xylene fraction containing from 70 to by volume of ortho-xyleneand from about 5 to 30% by volume metaand para-xylenes, said' process comprising the steps of converting orthoxylene of said fraction to phthalic anhydride by vapor phase oxidation in a phthalic anhydride forming zone with a vanadium oxide catalyst at phthalic anhydride forming temperatures, converting metaand para-xylenes of said fraction to combustion products readily separable from the phthalic anhydride by concurrently selectively over-oxidizingv said metaand para-xylene at least tothe point of ring rupture by vapor phase oxidation with a Vanadium oxide catalyst in said phthalic anhydride forming zone, passing saidvapor phase combustion products to a cooling zone, separating said phthalic anhydride from gaseous over-oxidation products' of said metaand para-xylenes by crystallization of phthalic anhydride in said cooling zone. and removing residual ring-rupture impurities condensed with the phthalic anhydride in the cooling zone by -gnstnlauon of the crystallized phthalic anhydride.

v5. A'process as deilne'dv in claim 4 in which said xylene fraction contains from about 80 to' about 90%by-volume ot ortho-xylene and from mixture of aliphatic substituted benzenes isa `xylene fraction containing'from '70' to 95% by volume ortho-xyleneiand from about 5 to 30% by volume meta-V` and para-xylenes; .s

8. A process.l ofv manufacturing phthalic an-A hydride from .a mixture of alkyl benzenes conin claim 1 'where-in said y v of ring rupture by vapor phase air oxidation with a vanadium oxide catalyst at a catalyst temperature of from labout 800 F. to 1175 F., passing said Vapor phase combustion products to a cool' -ing zone. separating said phthalic anhydride from vgaseous v over-oxidation products oi said metaand paraxylenes-by crystallization of phthalic anhydride in' saidI cooling zone, and removing re- Vsldual ring rupture impurities condensedwiththe phthalic anhydride in the cooling zone by distillation of the crystallized phthalic anhydride.

' l5 alyst support.

taining from about 70 -to about' 95% by volume of ortho' di-alkyl benzene having from 1 to'3 cari bon atoms in each alkyl group and from about 30 to about 5%v by volume of metaand para-dialkyl benzenes having from 1 to 3,-carbon atoms in each alkyl group. said process comprising the v steps of oxidizing the ortho di-alkyl benzene to phthalic anhydride and concurrently selectively over-oxidizing said metaand para-di-alkyl benzenes at least to the point of ring rupture by passing said mixture in a vapor phase over a vanadium oxide catalyst at a catalyst temperature of phthalic anhydride from said over-oxidized com ponents. l

9. A process as'dened in claim 8 wherein said mixture of alkyl benzenes is a xylene fraction.

, 10. A process as deilned in claim 8 wherein-said vvanadium oxide catalyst is non-porous.

11. A process of manufacturing phthalic an- A 12.\ A process as. dened in claim 11 wherein said vanadium oxide catalyst is non-porous..

13. A process as denned in claim 4 wherein the vanadium oxidecatalyst has a silicon carbide cat- 14. A process oi meta and para. xylenes, said process` comprising the steps of oxidizing the ortho Vxylene topthalic I t anhydrideL and simultaneously selectively overoxidizing meta andpara xylenes at least to the point of ring rupture bypassing said mixture in vapor phase over a vanadium oxide catalyst havfrom 800 F. to 1175 F., and separating said hydride from a xylenefraction containing from rl0'to 95% by volume of ortho xylene and from l,

about 5 to 30% by volume of metaand para- `xylenes which comprises the steps of converting ortho xylene of said fraction to phthalic anhydride by vapor phase air oxidation in a phthalic anhydride forming zone .with a vanadium oxide catalyst at a 4catalyst temperature'of from about 800 F. to about 1175. F. yand converting meta-4 and para-xylenes o1' said fraction to combustion Y products readily separable from the phthalic ani hydride byconcurrently selectively over-oxidizing said metaand para-xyleneat least to the point ing a, silicon carbide catalyst support, at a catalyst temperature 'of from-about 990 F. to about 1175 F., said concurrent oxidation reactionsV being effected with a molar excess'oi air in the ratio of'from about 50 to about 15o-mois of. air per mol of xylene mixture, and separating said phthalic anhydride from said oxidized gases.-

' IRVrNGE. LEVmE.

REFERENCES CITED The following references le of this patent: Y

f UNITED STATES PATENTS Number A Name Date 2,142,678 Porter Jan. 3. 1939 `2,114,798 Foster Apr. 9, 1'938 l OTHER REFERENCES F Mark and Hahn: Catalytic Oxid. of Org. Compounds in the Vapor Phase, page 395, Chem.

Catalog Co.

manufacturing pthalic anhydride by oxidation in vapor phase of amixture of Y xylenecontainin'g from-70% to 95% by volumeA .of orthoxyleneand from 30%-to about 5% of v are of record in the I 

